[CentOS] spam control

> I have found that greylisting based on the Spamhaus sbl-xbl list
> massively reduces spam. Setting that up on my backup MX
> resulted in all traffic through it stopping when my primary MX is
> up.
James,
Are you using greylisting or blacklisting with Spamhaus? My understanding
of blacklisting is that blacklisting uses a DNS blacklist, such as
Spamhaus. My understanding of greylisting is when your MTA sends back a
temporary failure the first time in X number of days where it sees a new
sender/receiver/mail server IP address triplicate. Please clarify.
Thanks,
Barry